Questions And Answers

Our paper lab is controlled to a 50% RH environment. Operators receive many uncomfortable shocks when touching the equipment and anything else metal such as the doorknob. Is a floor mat alone enough antistatic protection? I do not see us ever going to foot straps or wrist straps. Any advice? - Anonymous, Longview, WA

Answer

There are two highly probable reasons why your operators are experiencing ESD to metal conductors. One is triboelectric generation specifically caused by walking; the other is triboelectric generation caused by the friction of the cleanroom garments with the body or street clothes. Triboelectric generation (tribocharging) is a building up of an imbalance of charge on an object, caused by the action of contact and separation, and can lead to a physically perceptible ESD event. To minimize the first problem, an ESD floor mat that has the specific property of being antistatic may help as would an ESD floor finish systems. Our floor finish system has excellent antistatic properties, which from our experience does not allow tribocharging over 100 Volts. To minimize the second problem, have your operators wear cotton clothing versus rayon, nylon, silk, wool, etc. to minimize tribocharging of the body from the clean room garments rubbing on their street cloths or body. Wearing an ESD smock would help even more, providing an isolation of the dissimilar materials, some antistatic properties and being able to conduct charges. Also try clean room garments made from different materials, as the current materials making up the garments may be high (up or down) on the triboseries chart. As always, proper personnel grounding (ESD floor with foot grounders or wrist straps) is the sure way to eliminate your problems and would be our first recommendation.